Irreversible membrane fouling in microfiltration membranes filtering coagulated surface water

Chemical coagulation has been widely used as a method to mitigate membrane fouling in MF/UF membranes used for drinking water treatment. Optimization of coagulation as pre-treatment of membrane processes has not been achieved yet: the optimum condition of coagulation for conventional treatment systems is not necessarily applicable to membrane-based treatment systems. This study investigated (physically) irreversible membrane fouling in an MF membrane used with pre-coagulation by aluminum salt. In a series of bench-scale filtration tests, feed water containing commercially available humic acid or organic matter isolated from surface water was coagulated with polyaluminum chloride (PACl) under various conditions and subsequently filtered with an MF membrane with the nominal pore size of 0.1 μm. It was found that coagulation conditions had great impacts on the degree of physically irreversible fouling. Acidic conditions improved the quality of treated water but generally caused greater physically irreversible fouling than did neutral or alkaline conditions. Also, dosage of coagulant was found to be influential on the degree of membrane fouling: high dosage of coagulant frequently caused more severe irreversible fouling. Sizes of flocs seemed to become small under acidic conditions in this study, which was indicated by high concentrations of aluminum in the permeate under acidic conditions. It is thought that small flocs produced under acidic conditions could migrate into micropores of the membrane and caused physically irreversible fouling by plugging or adsorption. These findings obtained in the bench-scale tests were verified in a long-term pilot-scale test.     

Chiral Separations of Pyrethroic Acids Using Cyclodextrin Selectors

Pyrethroid insecticides are broadly used. They have low toxicity for warm-blooded living creatures, but high toxicity for both insects and fish. Therefore, it is important to reduce the environmental impact of pyrethroids. Pyrethroic acids are chiral compounds. An effective way to decrease pollution is to use enantio-pure insecticide products instead of their racemic mixtures. Enantiomer-pure products require enantiomer selective synthesis and analysis. The chiral selective analysis of pyrethroic acids (an intermediate of pyrethroids) is also important in terms of process control and from the point of view of their degradation metabolism in the environment. This study used various enantiomeric selective chromatographic methods for the separation of different pyrethroic acids, including gas chromatography, supercritical fluid chromatography and capillary electrophoresis. Systematic experiments were conducted to find the optimum conditions for their chiral separation. The employed enantio-selective agents were cyclodextrin derivatives with different ring sizes and substitution patterns. The β-cyclodextrin proved to be excellent for the chiral separation of these acids. The different chiral recognition mechanisms were established using different ring-sized cyclodextrins. The results of these systematic studies demonstrated the correlations of the chiral selectivity features of selectors and the structures of analytes.     

Light Hydrocarbon Separations Using Porous Organic Framework Materials

Light hydrocarbons (C₁–C₃) are used as basic energy feedstocks and as commodity organic compounds for the production of many industrially necessary chemicals. Due to the nature of the raw materials and production processes, light hydrocarbons are generated as mixtures, but the high-purity single-component products are of vital importance to the petrochemical industry. Consequently, the separation of these C₁–C₃ products is a crucial industrial procedure that comprises a significant share of the total global energy consumption per year. As a complement to traditional separation methods (distillation, partial hydrogenation, etc.), adsorptive separations using porous solids have received widespread attention due to their lower energy costs and higher efficiency. Extensive research has been devoted to the use of porous materials such as zeolites and metal-organic frameworks (MOFs) as solid adsorbents for these key separations, owing to the high porosity, tunable pore structures, and unsaturated metal sites present in these materials. Recently, porous organic framework (POF) materials composed of organic building blocks linked by covalent bonds have also shown excellent properties in light hydrocarbon adsorption and separation, sparking interest in the use of these materials as adsorbents in separation processes. This Minireview summarizes the recent advances in the use of POFs for light hydrocarbon separations, including the separation of mixtures of methane/ethane, methane/propane, ethylene/ethane, acetylene/ethylene, and propylene/propane, while highlighting the relationships between the structural features of these materials and their separation performances. Finally, the difficulties, challenges, and opportunities associated with leveraging POFs for light hydrocarbon separations are discussed to conclude the review.     

Strategy-Level Separations in Organic Synthesis: From Planning to Practice

A dirty word in synthesis: separation! The normally unavoidable separation at the end of each reaction finds no friends among synthetic chemists and is often regarded as a technical procedure. However, the need to quickly and cheaply produce pure products is driving the development of new separation and purification techniques. Astonishingly, the modern concepts and techniques for coupling synthesis and separation are rooted in workup procedures that are as old as the art of synthesis itself.     

Effect of coagulation conditions on the dewatering properties of sludges produced in drinking water treatment

The coagulation and flocculation processes in conventional drinking water treatment generate aggregates which settle to form a sludge waste. This sludge can be dewatered further by thickening, centrifugation and filtration operations in order to recover water and minimise the volume of the waste stream.A range of water treatment sludges generated in the laboratory were characterised according to a phenomenological method that is valid from the dilute free-settling regime to the concentrated cake compression stages. These were compared with plant samples.Experimental results show that raw water natural organic matter (NOM), coagulant dose and coagulation pH affected both the rate and potential extent of dewatering. Similar effects were observed for both aluminium sulfate and ferric chloride. These results suggest that increasing dose or pH leads to an increase in the proportion of rapidly precipitated material in the sludge or flocs, which form looser aggregates and hence exhibit inferior dewatering properties.     

Enantioselective Liquid Chromatographic Separations Using Macrocyclic Glycopeptide-Based Chiral Selectors

Numerous chemical compounds of high practical importance, such as drugs, fertilizers, and food additives are being commercialized as racemic mixtures, although in most cases only one of the isomers possesses the desirable properties. As our understanding of the biological actions of chiral compounds has improved, the investigation of the pharmacological and toxicological properties has become more and more important. Chirality has become a major issue in the pharmaceutical industry; therefore, there is a continuous demand to extend the available analytical methods for enantiomeric separations and enhance their efficiency. Direct liquid chromatography methods based on the application of chiral stationary phases have become a very sophisticated field of enantiomeric separations by now. Hundreds of chiral stationary phases have been commercialized so far. Among these, macrocyclic glycopeptide-based chiral selectors have proved to be an exceptionally useful class of chiral selectors for the separation of enantiomers of biological and pharmacological importance. This review focuses on direct liquid chromatography-based enantiomer separations, applying macrocyclic glycopeptide-based chiral selectors. Special attention is paid to the characterization of the physico-chemical properties of these macrocyclic glycopeptide antibiotics providing detailed information on their applications published recently.     

The Chemistry of Separations Ligand Degradation by Organic Radical Cations

Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexants and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R^•+), carbon-centered radicals (R^•), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R^•+ as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with various ligands. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved.     

Teicoplanin-Based Enantiomeric Separations in CZE Using a Partial Filling Technique

Baseline separation of the enantiomers of a number of negatively charged amino and mandelic acid derivatives was achieved in less than 10 min by capillary electrophoresis in a polyacrylamide coated capillary, using the “partial filling method” (PFM) with submillimolar concentration of Teicoplanin (TE) as the chiral selector. The influence of the charge and concentration of TE, electrolyte solution composition and pH, on the enantioresolution was examined. Further proofs were brought to corroborate the hypothesis that the enantiorecognition takes place at the D-Ala-D-Ala binding site, whose blockade is responsible for the antibacterial activity of glycopeptide antibiotics. While the dependence of the chiral recognition capabilities of TE on electrolyte solution composition and pH could limit its applicability, improved sensitivity, reduction of TE wall adsorption, resulting in a good efficiency, and high cost reduction, due to the very small amount of chiral selector required, were shown as advantages of the PFM adopted in this study.     

Ultra-Permeable Dual-Mechanism-Driven Graphene Oxide Framework Membranes for Precision Ion Separations

Two-dimensional graphene oxide (GO) membranes are gaining popularity as a promising means to address global water scarcity. However, current GO membranes fail to sufficiently exclude angstrom-sized ions from solution. Herein, a de novo “posterior” interfacial polymerization (p-IP) strategy is reported to construct a tailor-made polyamide (PA) network in situ in an ultrathin GO membrane to strengthen size exclusion while imparting a positively charged membrane surface to repel metal ions. The electrostatic repulsion toward metal ions, coupled with the reinforced size exclusion, synergistically drives the high-efficiency metal ion separation through the synthesized positively charged GO framework (PC-GOF) membrane. This dual-mechanism-driven PC-GOF membrane exhibits superior metal ion rejection, anti-fouling ability, good operational stability, and ultra-high permeance (five times that of pristine GO membranes), enabling a sound step towards a sustainable water-energy-food nexus.     

Mechanistic Principles in Chiral Separations Using Liquid Chromatography and Capillary Electrophoresis

Due to the importance of chiral separations of drugs, pharmaceuticals, agrochemicals and xenobiotics by high performance liquid chromatography (HPLC) and capillary electrophoresis (CE), it is important to have the knowledge of the enantiomeric recognition mechanisms so that scientists may design and module the new chiral selectors for rapid, inexpensive and reproducible chiral separations; specially at preparative scale. The mechanisms of the chiral separation by HPLC and CE using polysaccharides, cyclodextrins, macrocyclic glycopeptide antibiotics, Pirkle type, ligand exchangers, crown ethers and other several types of chiral selectors have been discussed. Various complex formation and different types of interactions responsible for chiral resolution have been presented in detail.     

Electrocatalytic Hydrogenation and Oxidation in Aqueous Conditions†

Water molecule contains one oxygen and two hydrogen atoms, making it a potential oxygen and hydrogen source. Electrocatalytic organic reduction and oxidation using water as oxygen and/or hydrogen donors provide an environmentally friendly and sustainable strategy to replace traditional chemical‐driven stoichiometric reactions that use sacrificial reagents. Furthermore, the development of electrochemical synthesis provides a potential application for low tension photoelectricity, which is not cost‐effective during boosted voltage and application. In the last decade, electrocatalytic redox reactions of organic molecules in aqueous media had shown progress owing to the development of electrode materials and water‐splitting technology. This paper highlights several electrocatalytic systems and corresponding mechanisms for both hydrogenation and oxidative transformation of representative compounds. The activation process of protons and water on the working electrode surface has received special focus. Furthermore, paired electrolysis using water as the oxygen and hydrogen source has been demonstrated. This paired system combines hydrogenation and oxidation half‐reactions in one cell using water as the hydrogen and oxygen source, resulting in high atomic and electron utilization rates.     

Reactions in Water – A Greener Approach Using Ruthenium Catalysts

Reactions using transition metals as catalysts have emerged as an efficient method in the recent times. However, the selection of solvent plays a crucial role in this regard. Several solvents used traditionally suffer majorly with problems of toxicity; high boiling point etc. leading to drastic reaction conditions. Water being a non‐toxic, non‐inflammable and environmentally benign can replace the hazardous organic solvents in laboratory as well as industry. Maintaining a minimum catalyst loading percentage we can advantageously avail high levels of selectivity. Water was found to be a good solvent medium for several metal catalysed reactions. An intramolecular deprotonation mechanism is followed by the ruthenium (II) catalysts in water; thereby, facilitating the catalytic action of the metal. These studies can help the industrial chemists to utilize water as a solvent for their reactions towards improvement of their waste management procedure. This review mainly focuses on the several recent developments in the above direction.     

磁性石墨烯@聚多巴胺纳米复合材料分离去除水中双酚A

本文通过水热法和多巴胺的自我团聚反应合成了磁性石墨烯@聚多巴胺(PDA@MG)纳米复合材料,该材料具有表面积大,含有丰富的π电子共轭体系、很好的水溶液分散性,易分离及可重复使用等特点。以PDA@MG为吸附剂材料,研究了其对水溶液中双酚A(BPA)的吸附性能。考察了吸附时间、温度、溶液的pH、吸附剂的用量等因素对该材料吸附性能的影响。结果表明在优化实验条件下,PDA@MG对BPA的最大吸附容量为151.3mg/g。PDA@MG具有优异的循环吸附性能,经过10次循环使用后其吸附能力没有明显减弱。